It is known in various connections to use valves that control the supply of a fluid by being opened when they are subjected to a certain pressure from the fluid. One such application is in wire line core drilling, as will be described below.
When performing exploratory drilling to collect rock samples from depths of from several hundred to a couple of thousand meters, double core tubes are used having an inner and an outer tube. The sample is collected in the inner tube, which usually has a length of a few meters. When the inner tube is full this is usually detected by means of a manometer or the like that measures the flushing water pressure in the core tube. A retriever device suspended on a wire is lowered into the tube for retracting the inner tube with the sample, said retriever device comprising a gripping means in the form of a claw or “spearhead” arranged to engage with a gripping means arranged on/in the upper end of the inner tube. When the wire is then tautened the inner tube is disengaged from the outer tube, and the inner tube with the sample can be hoisted up. Conversely, the claw and the gripping means on the inner tube can be used to lower a new inner tube. Equipment of this type is generally known as a wire line system.
When a new inner tube is inserted it is important to be able to ascertain that the inner tube really has reached right down to the bottom of the outer tube and has assumed its correct position for drilling, before drilling is commenced. Ascertainment that the tube can no longer move, but is firmly held is generally taken as an indication that the inner tube has reached its correct position. According to known technology, therefore, the gripping means is often designed to be combined with some type of locking member that firmly locks the inner tube in relation to the outer tube when the inner tube has reached the correct position. This locking member usually consists of a hook-like device, preferably spring-loaded, a locking claw or latch that engages with recesses or shoulders arranged in the inside of the outer tube. Actual insertion of the inner tube is usually performed by the inner tube being “pumped” along inside the drill string with the aid of water. When the inner tube is firmly in place the water pressure will increase to such an extent that a valve arranged for flushing medium in the inner tube is released.
One problem with such known arrangements is that when the inner tube is inserted into the drill string it sometimes catches before it has reached the correct position for drilling. With designs currently in use, the increase in water pressure then occurring will release the flushing valve before the inner tube has reached its correct position and, in the worst case, drilling will be commenced. This primarily entails a disadvantage from the financial point of view since the drilling will be into thin air. There is also a risk of the core at the bottom being destroyed. Hence it is useful to provide a landing indicator system in order to ensure that the inner tube has reached its correct position.
The current industry standard for a core barrel landing indication valve is to use a ball or plunger to pass through a plastic bushing, causing a brief increase in water pressure, indicating to the driller that the inner tube assembly has landed in the bottom of the hole. This signal is needed in core drilling to notify the driller when drilling can start.
As described in for example in CA2254040, fluid pressure pushes a valve member that is connected to a retracting case, through a bushing at an increased fluid pressure. However, in such prior art systems, the time the inner tube assembly takes to travel from the surface to the bottom of the hole is not productive and is increased due to the latches dragging against the inner wall of the drill string. Existing solutions also have reduced fluid flow due to the limited travel of the retracting case and by using the same ports for landing indication and drilling fluid flow.
Consequently, there is still presently a need for a valve assembly for a landing indicator system that offers better drilling fluid flow, while reducing drag of latches against the inner wall of drill strings.